The need for low-emissions fuels has created an increased demand for light olefins used in alkylafion, oligomerization, MTBE, and ETBE synthesis processes. In addition, a low-cost supply of light olefins, particularly propylene, continues to be in demand to serve as feedstock for polyolefin, particularly polypropylene production.
Fixed bed processes for light paraffin dehydrogenation have recently attracted renewed interest for increasing olefin production. However, these types of processes typically require relatively large capital investments and high operating costs. It is therefore advantageous to increase olefin yield using processes that require relatively small capital investment. It would be particularly advantageous to increase olefin yield in catalytic cracking processes.
A problem inherent in producing olefin products using FCC units is that the process depends on a specific catalyst balance to maximize production of light olefins while also achieving high conversion of the 650.degree. F.+(340.degree. C.+) feed components. In addition, even if a specific catalyst balance can be maintained to maximize overall olefin production, olefin selectivity is generally low because of undesirable side reactions, such as cracking, isomerization, aromatization and hydrogen transfer reactions. Light saturated gases produced from undesirable side reactions result in increased costs to recover the desirable light olefins. Therefore, it is desirable to maximize olefin production in a process that allows a high degree of control over the selectivity to C.sub.2 -C.sub.4 olefins.